Defrosting arrangement for refrigerating system



1959 E. c. SIMMONS 2,867,093

DEFROSTING ARRANGEMENT FOR REFRIGERATING SYSTEM Filed Dec. 20, 1955 2Sheets-Sheet 1 INVENTOR. Edward 6. Simmons BY WWW Jan. 6, 1959 E. c.SIMMONS 36 DEFROSTING ARRANGEMENT FOR REFRIGERATING SYSTEM I Filed Dec.20, 1955 2 Sheets-Sheet 2 GOOGOOOO 4 ()GGGCDCDO Fig. 5 INVENTOR.

fdwara' 6'. Sim/7700s United Sttes Fatent DEFRQSTING ARRANGEMENT FORREFRIG- ERATING SYSTEM Edward C. Simmons, Dayton, Ohio, assignor toGeneral Motors Corporation, Detroit, Mich., a corporation of DelawareApplication December 20, 1955, Serial No. 554,207

4 Claims. -(Cl. 62-152) This invention relates to refrigeratingapparatus and more particularly to an improved arrangement fordefrosting the same.

It is an object of this inventionto provide an improved arrangement forelectrically supplying heat to the evaporator of the frozen foodcompartment of a refrigerator in such a manner as to avoid localized hotspots.

More particularly, it is an object of this invention to attach a heaterelement to a relatively thin sheet or strip of metal which distributesthe heat uniformly throughout the sheet or strip, and then wrapping thesheet around the exterior of the freezer compartment evaporator.

Still another object of this invention is to provide an improvedarrangement for indicating to the user when the refrigerator is beingdefrosted. I

Another object of this invention is to provide an improved controlarrangement for the refrigerator and the defrost apparatus.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had .to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

In the drawings:

Figure 1 is a schematic view showing the refrigerant and electricalcircuits;

Figure 2 is a perspective view, with parts broken away, showing theconstruction of the defrost shield and its relationship to the frozenfood compartment evapo rator;

Figure 3 is a fragmentary developed plan View of the defrost shield;

Figure 4 is a fragmentary sectional view on an enlarged scale takensubstantially on line 4-4 of Figure 3;

Figure 5 is a fragmentary sectional view on an enlarged scale takensubstantially on line 55 of Figure 3; and

Figure 6 is a fragmentary sectional view taken substantially on line -6of Figure 2.

Referring now to the drawing, wherein a preferred embodiment of theinvention has been shown, reference numeral 10 generally designates arefrigerator having a frozen food storage compartment 12, an unfrozenfood storage compartment 14 and a machinery compartment 16. Therefrigerating system includes a first primary evaporator 13 which may beof any conventional construction and which forms the liner for thefrozen food storage compartment 12 in accordance with conventionalpractice. A second primary refrigerant evaporator 29 is mounted in theunfrozen food compartment 14 and is adapted to be connected inunrestricted series refrigerant flow relationship to the outlet of theevaporator 18 by means of the refrigerant line 22.

2,867,093 Patented Jan. 6, 1959 The outlet of the evaporator '20 isconnected to the suction line 24 which leads directly to the inlet of aconventional sealed motor-compressor unit 26 located in the machinerycompartment 16. The compressor 26 discharges the compressedrefrigerantdirectly into a super heat removing coil 28 which returns therefrigerant to the outer casing of the motor-compressor 26 inaccordancewith conventional practice. The motor-compressor casing is providedwithan outlet which delivers. the compressed refrigerant to the condenser 30wherein the refrigerant is condensed before discharging into the fixedres'trictor 32 which conveysjthe liquid refrigerant to the primaryevaporator -18. Systems of this type are more fullydescribed in Wurtz etal. Patent No. 2,672,020, to which reference is made for a more completedisclosure of the refrigerant circuit.

A defrost collecting pan 36 is disposed directly beneath the primaryevaporator 18 for collecting the defrost water .and for discharging thedefrost water through a drain 38 which leads to the condensatecollecting trough 40 located beneath the evaporator 20. The trough 40 isprovided with means 42 for directing the condensate water onto the. backwall of .the food storage compartment so as to cause the defrost waterto drain down along the back wall of the food storage compartment 14 andeventually enter the drain 44in the bottom wall of the compartment 14 soas to discharge thecondensate water into the vaporizer pan 46 located inthermal ex} change relationship with the relatively hot condenser 30, inaccordance with usual practice. The apparatus described thus far isintended to represent a conventional modern refrigeration system. t

The motor-compressor .unit 26 is adapted to be cycled by means of aswitch 50 which is controlled by means of a thermostat 52 located ontheevaporator 20. The thermostat 52 and the switch 50 are so designed andcalibrated that the circuit to the motor-compressor unit 26 will beclosed by the switch 50 when thetemperature at 52 exceeds 34 and willremain closed until the temperature at 52 drops to 2, at which time thecompressor is stopped until the temperature at 52 again reaches 34. Byvirtue of this arrangement, the evaporator 20 .will automaticallydefrost itself during each off cycle of the compressor, with the resultthat no auxiliary heat need be applied to the evaporator 20 fordefrosting the same, but this is not true of the evaporator 12, which ismaintained at temperatures of approximately .0" most of the time,irrespective of whether the motor-compressor unit 26 is energized, dueto the characteristics of refrigeration systems of this type, as morefully explained in the above-mentioned patent. The problem of defrostingthe frozen food compartment evaporator has been solved by this inventionby placing a specially constructed heating shield, or blanket, aroundthe top, bottom and sides of the evaporator 12 in direct intimatecontact therewith.

It is recognized that it is old to defrost evaporators by theapplication of heat thereto but in the prior art type of defrost heatersinadequate provision has been made for uniformly heating all parts ofthe evaporator in such a manner as to prevent hot spots in certainareas. It has been found that the freezer compartment evaporator 12 canbe defrosted very quickly at temperatures lower than formerly consideredpractical, by using a heater shield such as the shield 60, constructedin accordance with the -2,se7,oos

i i i' 3 showing of Figs. 2 through 5 of the drawing. Figure 2 shows theends of the heater shield 60 pulled away from the upper surface of theevaporator for purposes of illustration only. This shield consists of athin sheet or strip of aluminum or the like having a thickness ofapproximately .012" and having formed therein a plurality oftransversely extending heater wire grooves or passages 62 in which aninsulated heater wire 64 is placed, as best shown in Fig. 4 of thedrawing. The adjacent transversely extending portions of heater wire arearranged fairly close together, with the resultthat the heat generatedby current flowing through the wire 64 will uniformly heat the entireshield 60. The wire'64 is coated by means of insulation 66, which ispreferably a polyethylene material, which is not adversely affected bymoisture or temperature changes. It will be noted that the shieldenvelops a major portion of the insulated heater wire so as tofacilitate the transfer of heat from the wire to the aluminum shield andso as to hold the wire in place. It will also be noted that theinsulated heater wire does not directly contact the surface of theevaporator, with the result that there is less danger of hot spotsdeveloping in any one segment of the evaporator. That portion of theshield 60 which underlies the evaporator 18 is provided with waterdrainage holes 68 which allow the defrost water to flow into the pan 36.

As best shown in Fig. 6 of the drawing, the rear wall 69 of the foodcompartment 12 is provided with a flange 71 which overlies the rear edgeof the shield 60 so as to hold the shield against the evaporator plate18. Removable clamp elements 73 are bolted or otherwise secured to thefront edge of the evaporator plate 18 for holding the heater shield 60in place.

The power for operating the compressor and the defrost heater issupplied through the main power lines 70 and the energization of thedefrost heater is controlled by means of a switch 72 arranged in thecircuit, as shown. Theswitch 72 is a single pole, double throw switchwhich serves to open the circuit to the motor-compressor unit when thecircuit is closed to the defrost heater. This switch 72 is adapted to beoperated by means ofa timer 74 which opens the circuit to themotor-compressor unit and closes the circuit to the defrost heaterperiodically, such as once every week, for a predetermined period oftime such as fifteen minutes, so as to thereby heat the frozen foodstorage compartment evaporator 18 to a temperature high enough to meltall of the ice which may have formed thereon during the preceding week.

In the event that the temperature of the evaporator 18 exceeds apredetermined temperature such as 50 before the timer 74 opens thecircuit to the heater 64, a thermostat 76 which is arranged in thermalexchange relationship with the evaporator 18 serves to open the circuitat switch 78 located in the heater line, as shown, so as to preventunnecessary heating of the evaporator 18. The switch 78 recloses whenthe temperature of the evaporator drops below 35".

It has been found desirable to provide means for indicating to anyoneopening the door to the refrigerator whether or not the refrigerator isbeing defrosted at the time and in order to accomplish this, therefrigerator light 80 has been arranged in the circuit as shown, so asto be deenergized whenever the switch 72 has opened the circuit to themotor-compressor unit and has closed the circuit to the defrost heater.The light 8% is normally controlled by the door operated switch 82, inaccordance with conventional practice, so as to close the circuit to thelight $0 whenever the door is opened. By virtue of the abovedescribedcontrol circuit arrangement, it is obvious that this light 89 willremain off whenever the door is opened and the evaporator 18 is beingdefrosted. Y .1 By' virtue of the defrost heater construction describedherein, it is possible to place the heater wires close together and tooperate the heater at a much lower temperature and still obtain rapidand complete defrosting of the entire refrigerated surface. Insofar ascertain aspects of this invention are concerned, one could construct theshield in other shapes and sizes and could arrange the heating wire inother than the serpentine shape shown. Thus, the shield and the heatingwire could be so constructed and arranged that the heating wire wouldextend lengthwise of a long flexible shield which would be wrappedaround the outside of the evaporator. The shield in each instance servesas a means for holding the wire and for distributing the heat throughouta much larger area than would otherwise be possible.

While the form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, as may come within the scope of the claims whichfollow.

What is claimed'is as follows:

1. In a refrigerator having a storage compartment for food, anevaporator for refrigerating said food storage compartment, acompressor, a condenser, means for connecting said compressor,condenser, and said evaporator in series refrigerant flow relationship,heater means arranged in thermal exchange relationship with saidevaporator for defrosting said evaporator, said heater means comprisingflexible means wrapped around said evaporator and a heating elementbetween said flexible means and said evaporator, said heater elementbeing embedded in a groove provided in said flexible means, saidflexible .means having apertures therein beneath said evaporator for thedrainage of defrost Water.

2. In a refrigerator having a first storage compartment for frozen foodand a second storage compartment for unfrozen food, a first evaporatorfor refrigerating said frozen food storage compartment, a secondevaporator for refrigerating said unfrozen food storage compartment,

a compressor, a-condenser, means for connecting said compressor,condenser, first and second evaporators in series flow relationship,heater means arranged in thermal exchange relationship with said firstevaporator for defrosting said first evaporator, said heater meanscomprising flexible heat reflecting foil wrapped around said firstevaporator and a flexible heating element between said flexible 'foiland said first evaporator, said heating element being embedded ingroovesprovided in said foil, said heater being held out of contact with saidfirst evaporator by said foil.

3. Refrigerating apparatus including an above-freezing food compartmentand a below-freezing food compartment, a thermal heat transfer barrierbetween said compartments, a refrigerant liquefying means, a freezingevaporator means in heat exchange relation with said below-freezingcompartment and having its inlet connected to an outlet of saidliquefying means, a food compartment evaporating means in heat exchangerelation with said above-freezing food compartment and having its inletconnected to the outlet of said freezing evaporator means, means forreturning evaporated refrigerant from said freezing and food compartmentevaporating means to said liquefying means, thermostatic cycling controlmeans having a thermally sensitive element-responsive to the temperatureof said food compartment evaporattures, said below-freezing compartmenthaving a sufliciently slower heat-leak than said food compartment andsaid freezing evaporator means having sufliciently greater mass reiativeto said heat-leak than said food compartment evaporating means that saidbelow-freezing compartment is maintained at substantially constantsubfreezing temperatures during the cycling of said liquefying means,and means for cyclically supplying external heat to said freezingevaporating means so as to defrost the same at less frequent intervalsthan said food compartment evaporating means is defrosted.

4. In a refrigerator having a storage compartment for food, anevaporator for refrigerating said food storage compartment, acompressor, a condenser, means for connecting said compressor,condenser, and said evaporator in series refrigerant flow relationship,heater means arranged in thermal exchange relationship with saidevaporator for defrosting said evaporator, said heater means comprisingflexible means wrapped around said evaporator and a heating elementbetween said flexible means and said evaporator, said heater elementbeing embedded in a groove provided in said flexible means, saidevaporator having flanges overlying the edges of said flexible means soas to hold said flexible means in contact with the outer surface of saidevaporator.

References Cited in the file of this patent UNITED STATES PATENTS

